How to choose the right wires for electrical wiring and make a fuse. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook
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For the correct selection of the wire section, it is necessary to take into account the value of the maximum current consumed by the load. The current value is easy to determine, knowing the nameplate power of consumers according to the formula I \u220d P / 2000 (for example, for an electric heater with a power of 9 W, the current will be 60 A, for a 0,3 W light bulb - XNUMX A).
Knowing the total current of all consumers and taking into account the ratio of the current load permissible for an open wiring wire to the wire cross section (for copper wire 10 A per 1 mm, for aluminum 8 A per 1 mm), you can select a wire. When making hidden wiring (in a pipe or in a wall), the values given must be multiplied by a correction factor of 0,8. It should be noted that open wiring is usually performed with a wire with a cross section of at least 4 mm2, based on sufficient mechanical strength.
When choosing the type of wire, you must also take into account the permissible insulation breakdown voltage (it is impossible to use wires for a telephone line for electrical wiring for a mains voltage of 220 V).
The above ratios are easy to remember and provide sufficient accuracy for domestic use of wires. If you want to know with greater accuracy the long-term current load for copper wires and cables, then you can use Table 1.
Table 1
When wiring circuits at the input, it is imperative to install a general switch and fuses (fusible links or electromechanical machines). Fuses are the most widely used in household networks.
When a fuse blows, you need to quickly replace it, but there is not always a spare for the required current. In this case, a jumper ("bug") is often made from any wire that comes to hand. Over time, this is forgotten, and when overloaded, the wiring may catch fire.
To prevent this from happening, it is convenient to use a simplified formula that will allow you to correctly manufacture a fuse for any current with sufficient accuracy. For a single-core copper wire, the fuse protection current is determined by the simplified formula
Ipr = 80 (d3)1/2,
where d is the wire diameter, mm.
The results of calculations for different types of wires are given in Table 2.
Table 2
(click to enlarge)
Author: N.V. Mikheev
See other articles Section Electrician's Handbook.
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